ranzcrpart1fandomcom-20200214-history
Pituitary
The cavernous sinus (CS) is one of the paired dural venous sinuses. About 2cm x 1cm. It is usually a plexus of veins and not a trabeculated venous space. The cavernous sinus is located on either side of the pituitary fossa and body of the sphenoid bone in the middle cranial fossa, wrapped between the endosteal and meningeal layers of the dura. The normal lateral wall should be either straight or concave. Relations * Anterior: it is bounded by the superior ophthalmic fissure * P''osterior:'' petrous apex. * Roof: continuous medially with diaphragma sella. The ICA emerges from this surface. The uncus of the temporal lobe sits posteriorly. The third and fourth cranial nerves invaginate the roof here before passing into the lateral wall. * Floor: narrow strip of periosteum along the base of the greater wing of the sphenoid. * Lateral wall: continuous laterally as the inner layer of the dura across the middle cranial fossa with the temporal lobe sitting laterally. Posteriorly is Meckel's cave containing V3 mandibular branch and the anterior portion of the trigeminal ganglion. * Medial wall: fibrous lateral wall of the pituitary fossa and body of sphenoid (with the sphenoid sinus). Vascular connections It receives venous blood from: * Orbits - superior and inferior ophthalmic veins * Cerebral hemisphere - superficial middle cerebral vein: transverse the subarachnoid space and drain into the sinus by piercing its roof. * Vault bones - sphenoparietal sinus: runs just beneath the edge of the lesser wing of the sphenoid and enters the sinus through its roof. * Occasionally ** central retinal vein ** frontal tributary of the middle meningeal vein Drainage of the cavernous sinus is via: * superior petrosal sinus: leaves the top of the posterior end, pass over along the petrous bone, attached margin of the tentorium cerebelli, and enters the transverse sinus. * inferior petrosal sinus: leaves the posterior end of the sinus, runs down along the petrous bone and side of the clivus and enter the jugular foramen and directly into the jugular bulb. * venous plexus on the internal carotid artery to the clival (basilar) venous plexuses * emissary veins passing through the: ** sphenoidal foramen ** foramen ovale: communicates between the CS and pterygoid plexuses ** foramen lacerum * intercavernous sinuses: small plexus that lies between the two layers of dura of the floor of the pituitary fossa. Has anterior and posterior. Depending on relative pressures the superior ophthalmic veins either drain to or from the cavernous sinus. Contents Nerves The cavernous sinus transmits multiple cranial nerves to the superior orbital fissure and foramen ovale. These are: * In the lateral wall from superior to inferior: ** oculomotor nerve (CN III): enters the roof between the free and attached margins of the tentorium cerebelli, pass across the lateral wall, it picks up sympathetic fibres from the ICA, divide into its branches and traverse the superior ophthalmic fissure. ** trochlear nerve (CN IV): ''enters the roof behind the oculomotor nerves, alongside the ridge and course in the lateral wall. ** ''trigeminal nerve (CN V) ophthalmic and maxillary divisions. ''maxillary branch runs horizontal forwards in the lateral wall and leaves the middle fossa through the foramen rotundum. The ophthalmic divisions runs above the maxillary divisions and divides into its three branches towards the anterior end of the sinus. * Traversing the sinus: ** ''C4 segment of ICA ** abducens nerve (CN VI): enters the back of the cavernous sinus after passing over the apex of the petrous part of the temporal bone, lying inferolateral to the ICA. These can be remembered with the mnemonic OTOM CAT. Artery The internal carotid artery enters the posterior inferior aspect of the sinus from the foramen lacerum, and bends upon itself as the carotid siphon (cavernous segment - C4), emerging out of the roof of the sinus at the level of the anterior clinoid process. Two branches arise from this segment: meningohypophyseal trunk and inferolateral trunk. The artery is surrounded by a plexus of sympathetic nerves from the superior cervical ganglion. Clinical significance Danger area of the face, involves the angular vein and deep facial vein communicating to the cavernous sinus and to the superficial middle cerebral vein, allowing infection to pass from face to the cerebral hemisphere.